At 10 p.m., with 25 percent of the precincts reporting, Branstad and Grandy were neck and neck at 50 percent each. Democratic candidate Bonnie Campbell held an enormous 82 percent to 15 percent lead over opponent Bill Reichardt.

"It's going to be a long night," said an excited worker with the Grandy campaign, which gathered at the Ft. Des Moines Hotel.

In South Dakota's GOP primary, former two-term Gov. William Janklow appeared to hold the lead over incumbent Gov. William Dale Miller. A former lieutenant governor, Miller took over the job when Gov. George Mickelson, also a Republican, was killed in a plane crash last year.

With more than half the polls in by 9 p.m., Janklow had pulled ahead with 58 percent, a commanding 16-point lead over Miller.

The campaign has generated keen statewide interest. Joyce Hazeltine, South Dakota's secretary of state, was predicting a turnout of at least 35 to 40 percent. But by midafternoon Tuesday, some districts were reporting a turnout as high as 50 percent.

Some crossover voting was expected by those who either strongly dislike or like Janklow, who has a take-no-prisoners personality.

Miller, who has drawn the endorsements of present and former members of the state's congressional delegation, was leading Janklow by 7 points in one recent poll that showed he had made gains among undecided voters. But Janklow, a trial lawyer and former state attorney general, has dominated the stage in debates between the two. Unlike Iowa's contest, South Dakota's race has not driven a wedge among the state's Republicans.

Three South Dakota Democrats are competing for a chance at the winner, but by 9 p.m. Jim Beddow held a clear lead at 55 percent.

Incumbent governors in California, New Mexico, and Alabama also were facing upstart challengers from their own parties in Tuesday primaries.

California Gov. Pete Wilson, a Republican, appeared secure from an attempt by computer entrepreneur Ron Unz to take his job.

With heavy rains holding down voter turnout and nearly 20 percent of the polls reporting, Alabama Democratic Gov. Jim Folsom also appeared to be well ahead of Democratic challenger Paul Hubbert.

"It looks like the current governor may be successful. It doesn't look like we're going to be successful in getting all our voters to the polls," said Michael Tucker, press spokesman for Hubbert.

Hubbert, a lobbyist for the state teacher's association, has steered his campaign slightly to the right of the moderate Folsom, against whom he mounted an 11th-hour campaign that called into question the governor's ethics.

Folsom, a former lieutenant governor, took the reins from former Republican Gov. Guy Hunt, who was found guilty of campaign fund violations.

In New Mexico, three-term Democratic Gov. Bruce King faced two challengers, Casey Luna, an auto dealer who serves as King's lieutenant governor, and Jim Baca, an environmentalist who once ran the federal government's Bureau of Land Management. Baca, 48, also once served as King's press secretary.

Away from the governor's mansions, a pair of Senate incumbents-Democrat Frank Lautenberg of New Jersey and Republican Trent Lott of Mississippi-won renomination Tuesday.

Republicans were eyeing the results of Senate primaries in three states where Democratic incumbents-Lautenberg, Jeff Bingaman in New Mexico and California's Dianne Feinstein-are viewed, at least by the GOP, as vulnerable.

Republicans need a seven-seat turnaround in November to take control of the Senate for the first time since 1986 and are emboldened by the fact Democrats have lost Senate races in Texas and Georgia since President Clinton's election.

In New Jersey on Tuesday, GOP Assembly Speaker Chuck Haytaian won the right to face Lautenberg, a second-termer whose poll numbers are dismal.

Feinstein, who faced only token primary opposition, has been under fire from GOP Rep. Michael Huffington, the heir to a petroleum fortune who was favored in his GOP primary and has already spent $7 million trying to oust the incumbent senator.

In New Mexico, former Bush administration defense official Colin McMillan was favored for the GOP nomination to face Bingaman, who was heavily favored in his Democratic primary.

On the Republican side in the Senate, incumbent Sen. Conrad Burns of Montana, who earned just 52 percent of the vote in 1988, finds himself as a Democratic target this fall.

Two prominent Democrats, former Sen. John Melcher and lawyer Jack Mudd, have waged a testy primary campaign for the right to challenge Burns.

Primaries for House seats in California, New Jersey, Mississippi and Iowa also generated partisan interest.